Portable Catalytic Drying Apparatus

ABSTRACT

The present relates to a portable catalytic drying apparatus for use in applications such as drying, curing, polymerisation and cross-linking of organic coatings and compounds. The apparatus comprises a catalytic combustion chamber where a co-current lean mixture of fuel and air is combusted, a casing connecting a fuel supply to the combustion chamber, a regulating valve for controlling the flow of fuel, and an injector for mixing the fuel with air thereby providing a lean mixture of uniform fuel-air concentration.

FIELD OF THE INVENTION

The present application relates generally to drying devices, particularly where heat radiated from a catalytic combustion apparatus is used for drying, curing, polymerisation and cross-linking of organic coatings and compounds.

BACKGROUND OF THE INVENTION

There are in the current art apparatuses for surface emission of infrared radiation, with catalytic combustion of a mixture of a combustible gas (for example a gaseous hydrocarbon such as natural gas, propane or butane) with an oxidizer gas such as air. Catalysts used in such apparatuses typically include noble metals such as platinum, palladium or rhodium group metals or compounds containing the same. The substrates upon which the catalysts are supported are typically made from refractory fibers.

Generally, a drawback of such known apparatuses is that they are not portable, being rigidly attached to the walls or ceiling of a stationary oven. Under such conditions, pieces to be dried, cured, polymerised or cross-linked must either be placed in the range of the apparatus before treatment starts as in a batch oven, or must be continuously brought into the range of the apparatus as in a tunnel oven. Furthermore, catalytic combustion apparatuses currently available contain complex control panels which add substantially to the cost of drying, curing, polymerisation and cross-linking.

SUMMARY OF THE INVENTION

The present disclosure is generally directed to a portable catalytic drying apparatus for applications such as for example drying, curing, polymerisation and cross-linking of organic coatings and compounds. The present portable catalytic drying apparatus comprises a a portable casing, a regulating valve, an injector and a catalytic combustion chamber. More particularly, the catalytic combusion chamber comprises a perforated diffuser plate, a ceramic insulation blanket, a porous pad impregnated with catalytic material and a heat protection grille, in which a co-current lean (for example with 45% excess air) mixture of fuel and air is combusted. The portable casing is adapted for connecting to a fuel supply. The regulating valve controls the flow of fuel, while the injector mixes the fuel with air so as to obtain the lean mixture of uniform fuel-air concentration. The present portable catalytic drying apparatus may further comprise moveable handles and/or straps enabling easy and flexible carrying and positioning of said apparatus.

In a particular aspect, the apparatus may be installed on a fixed tripod.

In another aspect, the apparatus is small and lightweight enough to be manually handled, used and operated by a single person. In another aspect, the present apparatus is completely autonomous. This portability makes it much easier to carry and position the apparatus to, for example, make touch-ups or treat difficult-to-reach parts in automotive paint shops. Furthermore, the apparatus can be attached to a base equipped with piezoelectric means for igniting the fuel-air mixture before the apparatus is used, in such a manner that even if the apparatus is operated inside a hazardous location, for example a Class 1, Division I location, its ignition base remains outside hazardous locations at all times. This provides an advantage because the ignition base does not need to be certified for operation in hazardous locations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation view of an exemplary embodiment of a drying apparatus.

FIG. 2 is a side perspective view of an exemplary embodiment of a drying apparatus.

FIG. 3 is another side elevation view of an exemplary embodiment of a drying apparatus.

FIG. 4 is an exploded view of the portion of an exemplary embodiment of the drying apparatus which connects to the combustion chamber.

FIG. 5 is an exploded view of the combustion chamber of an exemplary embodiment of the drying apparatus.

FIG. 6 is a side elevation view of an exemplary ignition base of with the present drying apparatus.

DESCRIPTION OF EMBODIMENTS

Referring now to FIG. 1, an exemplary embodiment of a drying apparatus 10 is shown, in which a fuel, such as for example propane or butane, is supplied under pressure from a removable fuel canister 6 to a combustion chamber 1 containing a catalyst-containing substrate where the fuel reacts with oxygen. The fuel-air mixture is lean, having typically 45% excess air. Catalysts used in such devices typically include noble metals such as for example platinum, palladium or rhodium group metals or compounds containing the same. The substrates upon which the catalysts are supported are typically made from refractory fibers. The catalytic substrates generate a flameless combustion with surface emission of infrared radiation in the controlled wavelength range between approximately 2 μm and 10 μm where radiation is most easily absorbed by organic coatings and compounds for the purposes of drying, curing, polymerisation and cross-linking. The term “surface emission” should be understood to mean a surface emitting, at substantially every point, infrared radiation, with a calorific emission power distributed substantially homogeneously and substantially uniformly over the emitting surface.

FIG. 1 also shows a grille 2, which provides thermal protection from said combustion chamber, a casing 5, made of a lightweight material such as plastic, connecting the fuel supply to the protective grille, and moveable handles 7 and straps (not shown) enabling easy and flexible carrying and positioning. The apparatus is small and lightweight enough to be handled, used and operated by a single person, and may be completely autonomous. In this exemplary embodiment, the surface of the catalytic combustion chamber is of round shape, of a diameter of 12 inches (305 mm) and of a drying power of 6000 BTU/hr (1.76 kW). However, other shapes, surfaces and drying power could also be used without departing from the scope of the present disclosure.

FIG. 2 is a side perspective view of an embodiment of the drying apparatus 10, showing a more detailed view of the front of the combustion chamber 1 and the protective grille 2, and showing the location of a regulating valve 4 located between the fuel supply 6 and the combustion chamber 1.

FIG. 3 is another side elevation view of an embodiment of the drying apparatus 10, showing a more detailed view of the emitting surface at the front of the combustion chamber 1.

FIG. 4 is an exploded view of the portion of an exemplary embodiment of the drying apparatus 10 which connects to the combustion chamber 1. In this exemplary embodiment, the fuel canister 6 is threadedly engaged to the regulating valve 4. The regulating valve 4 comprises a rotary-actuator-controlled, spring-loaded regulator which reduces fuel pressure. After discharge from the regulating valve 4, the fuel enters an injector 3, creating a negative pressure gradient relative to the atmosphere. Air enters the injector 3 from one or several holes drilled on its side, and is mixed with the fuel to obtain a lean (typically with 45% excess air) mixture of uniform fuel-air concentration. The fuel-air mixture then proceeds to the combustion chamber 1. Adjustable handles 7 allow the user to position the apparatus and direct the radiation towards the material to be dried, cured, polymerised or cross-linked. In addition, adjustable straps (not shown), fastened around the axes of rotation of the handles, may go around the user's back to improve portability. The drying apparatus 10 may be portable, lightweight enough to be manually handled, used and operated by a single person, and completely autonomous.

FIG. 5 is an exploded view of the combustion chamber 1 of an embodiment of the drying apparatus 10. The combustion chamber 1 comprises a connecting tube 11 for transferring the fuel-air mixture from the injector 3, a crimping ring 12, a back pan 13, a perforated diffuser plate 14, a tightness ring 15, a first ceramic fiber blanket 16, a second ceramic fiber blanket 17, a porous pad 18 impregnated with catalytic material where the co-current lean mixture of fuel and air is combusted, a surface grille 19 and a front ring 20. In one particular embodiment, the ceramic fiber blankets 16 and 17 consist of spun fibers of alumina and silica, with a thickness of 12.5 mm and a bulk density of 96 kg/m³. The porous pad 18 is made of nearly pure alumina fibers with a mean fiber diameter of 3.5 microns and specific surface between 150 and 200 m²/g. When ignited, the lean mixture used in the present apparatus provides an emitting surface temperature of around 1000° F., which allows the emitting surface to radiate in a controlled wavelength range between approximately 2 μm and 10 μm, where radiation is most easily absorbed by organic coatings and compounds for the purposes of drying, curing, polymerisation and cross-linking. If the air-fuel mixture were stoichiometric, rather than lean, the emitting surface temperature could be much higher and radiation emitted from a surface at this higher temperature would not be absorbed as easily by the object to be dried, leading to possible scorching or formation of bubbles within the paint or coating, which is not desirable for the applications currently considered.

An implementation of the present apparatus was used and tested. Tests were made to determine the temperature distribution on the emitting surface, as well as on a typical target. In the first series of tests, an infrared thermometer was used to determine temperature along horizontal and vertical centerlines of the emitting surface. The apparatus was oriented horizontally. The results, shown in Table 1, establish that the apparatus has an emitting surface temperature near 1000° F. which allows it to radiate in the controlled wavelength range between approximately 2 μm and 10 μm.

TABLE 1 Temperature distribution on emitting surface of apparatus. 6″ left 4″ left 2″ left Center 2″ right 4″ right 6″ right 6″ higher  896° F. 4″ higher 1008° F. 2″ higher 1020° F. Center 1018° F. 1004° F. 1020° F. 1020° F. 1004° F. 958° F. 934° F. 2″ lower 1000° F. 4″ lower  915° F. 6″ lower  896° F. Average: 976.4° F.

The second series of tests were for the purpose of measuring the temperature increase in a typical object to be dried. A 22″ diameter circular panel was cut out from an automobile hood and painted with black automobile paint. The axis of the automobile panel and of the drying apparatus were lined up horizontally, with the painted side of the automobile panel facing the drying apparatus, at a distance 18″ from it. Six (6) thermocouples were screwed upon the surface of the automobile panel. The thermocouples were located as follows:

1. On the side facing the drying apparatus, in the center of the panel; 2. On the side facing the drying apparatus, at the right end of the panel; 3. On the side facing the drying apparatus, at the bottom end of the panel; 4. On the side facing the drying apparatus, at the left end of the panel; 5. On the side facing the drying apparatus, at the top end of the panel; 6. On the side opposite the drying apparatus, in the center of the panel.

The evolution of the temperatures measured by the thermocouples after ignition is shown in Table 2.

TABLE 2 Temperature distribution on automobile panel targeted by apparatus. Thermocouple #, ° F. Elapsed time, min 1 2 3 4 5 6 Average 0 73 73 72 72 72 71 72.2 1 94 93 89 89 89 80 89.0 2 112 108 101 102 103 93 103.2 3 127 119 111 111 115 105 114.7 4 137 126 116 116 124 114 122.2 5 143 130 119 120 130 120 127.0 6 148 132 121 123 134 124 130.3 7 151 135 123 126 138 128 133.5 8 154 137 125 128 141 131 136.0 9 157 138 126 130 144 134 138.2 10 157 138 126 130 145 133 138.2 Average after 10 minutes: 138.2° F.

The results provided in Table 2 establish that the target absorbs radiation efficiently and quickly reaches a temperature near 140° F., ideal for drying.

FIG. 6 is a side elevation view of an ignition base 8 of an embodiment of the drying apparatus 10. For lighting, the protective grille 2 of the drying apparatus 10 is set to rest on notches 20 in the body of base 8. The base 8 comprises a slideable and rotatable flame cover 9. When the flame cover 9 is vertically engaged on the combustion chamber 1, a piezoelectric mechanism (not shown for clarity purposes) on the ignition base automatically ignites the drying apparatus 10. The ignition base 8 is not limited to the shape and proportions shown on FIG. 6, which is used only for graphical representation purposes, and to demonstrate that the ignition base 8 may be separated from the apparatus 10 to allow ignition in secure area, while the present drying apparatus 10 may be used when ignited in areas where hazardous products are used. 

1- A portable catalytic drying apparatus comprising: a portable casing for connecting to a fuel supply and for receiving fuel therefrom; a regulating valve for controlling the flow of fuel from the fuel supply; an injector for mixing the flow of fuel with air thereby providing a co-current lean fuel-air mixture; a combustion chamber comprising a protection grille, a perforated diffuser plate, a ceramic insulation blanket and a porous pad impregnated with catalytic material where the co-current lean mixture of fuel and air is combusted; whereby after ignition of the fuel-air mixture in the combustion chamber, the portable catalytic drying apparatus generates heat. 2- The apparatus of claim 1, comprising moveable handles and adjustable straps enabling easy carrying and positioning. 3- The apparatus of claim 2, wherein the portable catalytic drying apparatus is lightweight enough to be manually handled, used and operated by a single person, and completely autonomous. 4- The apparatus of claim 1, wherein the apparatus can be attached to a base equipped with piezoelectric means for igniting the fuel-air mixture before the apparatus is used; 5- The apparatus of claim 1, wherein a co-current mixture of fuel and air typically with 45% excess air is combusted. 